This invention relates to amplifying schemes which use a number of amplifiers to provide output voltage and power swings greater than those available from a single amplifier.
It is known to cascade amplifiers in series, parallel, or in series/parallel combinations, to increase the overall voltage swing and power output of the amplifier arrangement without increasing the magnitude of the power supply voltages, and also to facilitate impedance matching to loads.
In some arrangements, for example, those described in U.S. Pat. No. 4,454,480, issued to Allfather et al., identical amplifiers are cascaded between a common (e.g., ground) terminal and an output terminal. Each amplifier includes a dual polarity power supply, the common (i.e., reference) node of which is driven by the output of the immediately preceding amplifier in the cascade arrangement. A signal to be amplified is applied in series to the inputs of the amplifiers. Typically, the signal is applied between the common node of each amplifier's power supply and the input of the amplifier using an isolation amplifier or an isolation transformer. Because each signal is referenced at the same potential as the power supply of the amplifier to which the signal is applied, the source of the signal to be amplified must be capable of producing voltage swings that are greater than the voltage swings generated by a single amplifier.